Field of the Invention
The present invention relates to an actuator that drives by causing a vibrator to generate an elliptical vibration to cause a friction member to move with respect to the vibrator.
Description of the Related Art
An actuator has been conventionally used as a driving source of, for example, a camera or a lens, to take advantage of characteristics thereof such as silent operation, a driving capability from a low speed to a high speed, and a high torque output.
For example, Japanese Patent Application Laid-Open No. 2011-254587 discloses an ultrasonic motor as an actuator that includes a friction member and a vibrator including a vibration plate and a piezoelectric device. The vibrator is arranged in a friction-contact condition in which the vibrator is pressurized by the friction member. When an ultrasonic vibration is excited in the vibrator that is in the friction-contact condition, an elliptical motion arises at a portion of the vibrator that is in contact with the friction member, and a relative movement is performed between the friction member and the vibrator.
The vibrator includes support portions that extend from two side surfaces in a symmetrical form, and one part of each support portion is fixed to a vibrator holding member. Further, a piezoelectric device is bonded to one side of a rectangular part at a center portion of the vibration plate, and two projections are formed on opposing surfaces and contact the friction member with friction.
In general, when fixing a piezoelectric device on a vibration plate, a surface on which the piezoelectric device is to be fixed is finished into a uniform flat surface from which concavities and convexities, warping, burrs and the like are removed by a polishing process, and fixing is then performed using an adhesive or the like. As a result, the piezoelectric device can be closely adhered to the vibration plate, and a deformation that arises in the piezoelectric device can be reliably transmitted to the vibration plate.
However, with the ultrasonic motor disclosed in Japanese Patent Application Laid-Open No. 2011-254587, there is the problem that if warping, concavities and convexities, a deformation or the like arise in the vibration plate, a large amount of time is required to perform the polishing process, and furthermore the vibration plate becomes an irregular shape after the polishing. In particular, since the rigidity of the support portions of the vibration plate of the vibrator is low, warping or deformation is liable to occur. In a case where the support portions become warped in a manner such that the support portions protrude to the surface side or are deformed, there is the problem that, when polishing the vibration plate, an area from the vicinity of the support portions is polished first, and hence the overall form of the vibration plate becomes a semi-cylindrical shape. This leads to a decrease in the performance of the ultrasonic motor, such as a drift or variations in the resonance frequency of the vibration plate.
In the ultrasonic motor disclosed in Japanese Patent Application Laid-Open No. 2011-254587, no consideration is given to the method of manufacturing the vibration plate, and in the case of using compression molding that is a generally inexpensive manufacturing method, burrs and warping are liable to arise, and consequently the above described problems occur.